Tar sands or bituminous sands are well known in various parts of the world. Most important deposits have been discovered in Alberta, Canada, along the Athabasca River. These particular tar sands are known as Athabascan tar sands and contain a large amount of the world's known reserves of crude oil. These tar sands may generally be characterized as comprising particles of silica surrounded by a water envelope which is in turn surrounded by the tar. The tar sands may additionally contain various forms of silt and clay. In general, tar sands may contain from 5 to 21% by weight of oil which may vary from 6 to 10 API gravity. It has been difficult to separate the oil from tar sands and in the past the economy of the process was the most critical parameter for commercialization. There have been two methods in use for the separation of tar sands; the hot water process and the cold water process. The hot water process relies on jetting steam and a minor amount of hot water at a temperature of 170.degree. to 190.degree. F. through ground up tar sands to form a slurry. In this process, the sand settles to the bottom of the slurry while the oil rises to the top in the form of a froth which is separated as an emulsion of the oil and the water. The breaking of this emulsion so as to recover the oil has caused great difficulty with this process.
In the cold water method, as, for example, disclosed in U.S. Pat. Nos. 2,825,677 and 3,041,267 a solvent is first added to the ground up tar sand to dissolve the bitumen. This solvent slurry is then introduced into a large volume of water which may comprise a salt or a surface active agent. The oil is then separated along with the solvent from the water and sand by pressure or gravity.
More recent developments in separating the bitumen from tar sand have relied on the use of solvent systems, including single solvents, multistep processes where the tar sand is contacted with different solvents in serial steps, and multisolvent systems where the solvent is tailored to dissolve the bitumen alone or the bitumen along with the asphaltenes. The various solvent processes, as stated above, either remove all of the oil by extraction with an aromatic solvent or a bitumen portion, only, by extraction with a paraffinic type solvent. For example, in U.S. Pat. No. 3,475,318, a process is taught for extracting a bitumen low in asphaltenes by using a saturated hydrocarbon solvent having from 5 to 9 carbon atoms per molecule, or alternatively adding up to 20% of an aromatic having from 6 to 9 carbon atoms per molecule to separate the asphaltenes along with the bitumen. In a later step of the invention, these asphaltenes must be separated from the solvent-bitumen fraction. It is noted that the patentee teaches that the bitumen, if present, in admixture with asphaltenes must be vacuum flashed in an additional separation step. Furthermore, the patentee, since he relies on a filtering operation, to separate the oil from the sand does not recognize the advantage of separating the asphaltenes from the sand in other than a dissolved form. See also U.S. Pat. No. 3,459,653 which teaches use of a deasphalting solvent to remove bitumens and leave asphaltenes on the sand.
It should be noted that when the asphaltenes are left on the sand, steam must be used to separate the solvent associated with the sand. The use of warm water, as disclosed below in the description of the instant invention results in the formation of stable emulsions, from which the solvent is difficult to recover.
Other tar sand extraction processes which rely on aromatic solvents to remove substantially all the bitumens and asphaltenes, in a single step, from the sand include those described in U.S. Pat. No. 2,965,557 wherein gasoline is used to remove the oil from the sand; U.S. Pat. No. 3,117,922 wherein a heavy oil high in aromatic content is used and the patentee is careful not to form an asphaltene phase in his extraction step; U.S. Pat. No. 3,392,105 wherein the patentee mixes gasoline, isopropanol and water to create a slurry, said slurry being further diluted with gasoline, isopropanol, phenol, furfural, liquefied petroleum gases, etc.; and U.S. Pat. No. 3,553,099 wherein toluene is used to extract the oil from the sand and thus substantially all the oil associated with the sand is separated as a solution from said sand.
In an article by D. L. Mitchell et cl, FUEL, 1973, Vol. 52, April, pages 149-152, the solubility of asphaltenes in various solvent is disclosed. It is noted in the article that aromatic solvents dissolve all asphaltenes while the paraffinic solvents do not.
In U.S. Pat. No. 2,871,180 a process is disclosed wherein tar is separated from tar sands in two fractions. The patentee pulps the tar sand with water and steam to disrupt the oil and water phase which surrounds the sand particles and then contacts the pulped sand with a deasphalting solvent which contains less than 6 carbon atoms. The asphaltene phase separates from the deasphalting solvent-bitumen phase by gravity, the asphaltene phase being present as a liquid phase comprising a substantial amount of the bitumen associated therewith. The sand and water are removed from the bottom of a settling tower while the oil is removed from the tower in the two fractions described. The patentee recommends the use of propane, thus allowing the asphaltenes to take a certain amount of the bitumen along therewith. Furthermore, since the patentee teaches the breaking of the water envelope during the pulping of the sand, he loses a substantial amount of solvent along with his sand and water. Finally, it is known in the art that the use of propane in the extraction of bitumen requires high pressure and temperature conditions, thus necessitating increased expenditures for the special equipment used in carrying out the process.